Reconditioning a Relmac lathe

[Robin Hewitt]

Cuttlefish bone is clear proof that God does low temperature metal casting. If He didn't why would anything so wonderful exist.

You can sand it flat in a trice, push things in and it takes the shape, doesn't bend, soaks up dross, doesn't melt, doesn't distort when hot, lets trapped air out at the join and has no thermal inertia :D

[irving2008]

and where would I buy it???

[Robin Hewitt]

True, budgies trim their beaks on it, but the big ones go to the goldsmiths. Any problems finding it I can get it off the beach, just have to wait for an onshore wind. We have a thriving cuttlefish population. It weighs nothing :D

It has a thin horny rind on one side, the good stuff is in the middle. Pure white.

[irving2008]

Well its been a while but last weekend I finally managed a further 2 attempts at pouring this bearing (getting a dab hand at setting it all up now)...

Anyway, got what I was fairly sure was a good one - I used a digital temperature probe from Maplins (£19.99, also doubles as a cheap multimeter to keep in the garage to save my very expensive one getting damaged) to measure the temperature inside the spindle and heated everything til that was 220degC. But it takes an hour or more to cool down to be able to be touched and I didnt have time to get the spindle out then. But I was working at home today so took an hour or so out this evening to get the spindle out (blowtorch needed to exapnd things a little to free it off) and start the clean up.

I am mightily impressed with the result....





This is after I cut and tidied up the slot (which makes it easy to get the spindle in and out now) and about 1/2 way filing down the excess on the bearing ends. The bearing is so close that 1/4 of a turn on the pinch bolt goes from 'mildly stiff to turn' to 'locked spindle' and the play is <.0005" on the DTI...

Next job is to clean up the ends and then do a spot of scraping on the bearing surface (although I am hesitant to do too much of that, in fact I am tempted not to do any right now since its so tight and the journal is freshly ground)

Looks like I'll have a working lathe in a few weeks....

[Lee Roberts]

Any advances on this mate?

[irving2008]

Hi Lee,

Been away on hols, just got back tonight.

Had the lathe up and running but got to sort out some vibration which I think is due to the rear bearing . the new front one is fine and run in now. The other prob I have is that the runout on anything held in the chuck is massive - think a new chuck is needed.

[Lee Roberts]

ahh i c, is a new chuck going to be a problem or are they quite generic?

[irving2008]

Lee,

The chuck isn't the issue... machining a new backplate may well be because of the non-standard spindle thread (1.25" x 12tpi).... I'll probably need to get it done professionally :(

[m_c]

Why not remachine the existing back plate?

Unless you need to remove a lot of metal to make it suitable for a new chuck, then it should be fine.

[irving2008]

Why not remachine the existing back plate?

Unless you need to remove a lot of metal to make it suitable for a new chuck, then it should be fine.

Because a modern chuck requires a larger boss. Currently it has a 4" chuck with a 3" recess but modern 100mm chucks have an 80mm recess. Also there is possibly a problem with the backplate itself, but until I can clamp it up on a known good machine to measure both axial and radial runout accurately I can't be sure...